[unreadable] T cells are central to the pathogenesis of the inflammatory bowel diseases, which include ulcerative colitis (UC) and Crohn's disease (CD). While UC involves strictly the large intestine; CD involves predominantly the small bowel. Therefore the recirculating lymphocyte pool must express a defined repertoire of adhesion molecules and chemokine receptors that allows recognition of these 2 intestinal segments. Our understanding of the specific molecules that mediate differential trafficking to small or large bowels is limited, in part due to the lack of animal models that develop inflammation specifically in the small intestine. Our long-term goal is to dissect the adhesive pathways responsible for lymphocyte trafficking to the chronically inflamed small bowel using a novel murine model (i.e. SAMP1/Yit). Our specific hypothesis is that chronic inflammation induces inappropriate expression of adhesion molecules, supporting continuous dysregulated recruitment of pathogenic T cells to the small bowel. Our recent findings shed light on 2 concepts that appear pivotal to our understanding of small intestinal trafficking. First, effector T cells coexpress not only the gut-homing integrin alpha4beta7, abut also the peripheral homing integrin alpha4beta1 and L-selectin. These L- selectin(positive) cells are important producers of TNF-alpha and targeted immunoblockade of this molecule attenuated ileitis. Based on these observations our experimental focus is on L-selectin-mediated lymphocyte recruitment to the small bowel. Our specific aims will: [unreadable] 1. Determine whether effector CD4+ T cells re-express L-selectin to recirculate to the small intestinal lamina propria (LP). We will (i) assess whether CD4+ T cells reexpress L-selectin using fluorescent cell homing assays. (ii) Functionally assess the capacity of L-selectin(negative) compared to L-selectin(positive) T cells to adoptively transfer ileitis via T cell transfer and histological assessment of the severity of ileitis. [unreadable] 2. Define the small intestinal endothelial ligands responsible for the therapeutic effect of L-selectin immunoblockade in chronic murine ileitis. We will perform therapeutic studies designed to assess the contributions of i) MAdCAM-1and ii) PNAd as specific endothelial ligands for L-selectin in the chronically inflamed small bowel. [unreadable] 3. Identify the cellular and molecular mechanisms responsible for the efficacy of L-selectin/MAdCAM-1 blockade as therapeutic targets in chronic ileitis. We will (i) define the role of L-selectin, alpha4beta1, alpha4beta7 integrins and MAdCAM-1 along the adhesion cascade using intravital microscopy. ii) Determine the time course of HEC-6 sulfotransferase induction through adoptive T cell transfer, Immunohistochemistry and real time RT-PCR. [unreadable] Given the similarities between the small intestinal-specific disease of the SAMP1/Yit model and human CD, our studies may shed light on the mechanisms that determine trafficking of effector T cells specifically to the small bowel and potentially identify new molecular targets for the treatment of CD. [unreadable] [unreadable]